In recent years, as an image display optical system of this type, one that ensures a wide exit pupil and a wide angle of view has been proposed (see, e.g., Japan Unexamined Patent Application Publication No. 2003-536102.). For example, in the image display optical system described in FIG. 2 of JP 2003-536102, a plurality of partially reflecting surfaces parallel to one another is provided inside a transparent plane substrate. An image-carrying light flux emitted from an image display device, such as a liquid crystal display device, is introduced into the inside of the plane substrate in a state of being formed into a parallel light flux.
The image-carrying light flux introduced into the inside of the plane substrate propagates through the plane substrate while reflecting internally after deflected at a reflecting surface (symbol 16 in FIG. 2 of JP 2003-536102). The image-carrying light flux that propagates through the plane substrate enters the plurality of partially reflecting surfaces (symbol 22 in FIG. 2 of JP 2003-536102) sequentially. Each image-carrying light flux that has entered each partially reflecting surface at the same angle to one another is deflected by the same angle, respectively, and is emitted to the outside of the plane substrate.
As a result, outside the plane substrate, a comparatively large region that the image-carrying light flux with each angle of view emitted from each position of the image display device enters in an overlapping manner is formed. If the pupil of the eye of a viewer is placed at any point in the region, it is possible for the viewer to view the virtual image of the image display device. In other words, this region serves as an equivalent of an exit pupil. Hereinafter, this region is referred to as the “exit pupil”.
It is possible to easily extend the exit pupil by increasing the number of partially reflecting surfaces to be arranged. If the exit pupil is wide, the degree of freedom of the position of the pupil of a viewing eye is increased, and therefore, a viewer can view in a more relaxed state. In addition, in FIG. 2 of JP 2003-536102, the image-carrying light flux is drawn as one broken line, however, the actual image-carrying light flux includes each image-carrying light flux with each angle of view.
The image-carrying light flux with each angle of view is introduced into the inside of the plane substrate at different angles and propagates through the plane substrate at different angles while being reflected internally. Consequently, depending on the opening angle of the light ray of the image-carrying light flux that propagates through the plane substrate, the angle of view of the image display optical system is determined. In addition, in the image display optical system, since the propagation path of the image-carrying light flux is folded inside the plane substrate, the opening angle of the light ray capable of propagating through the plane substrate becomes larger than that when not folded.
Consequently, it is possible to ensure a wide angle of view in this image display optical system.